The use of cellular communication systems having mobile devices which communicate with a hardwired network, such as a local area network (LAN) or a wide area network (WAN), has become widespread. Retail stores and warehouse, for example, may user cellular communications systems with mobile data terminals to track inventory and replenish stock. The transportation industry may use such systems at large outdoor storage facilities to keep an accurate account of incoming and outgoing shipments. In manufacturing facilities, such systems are useful for tracking parts, completed products and defects. Such systems are also utilized for cellular telephone communications to allow users with wireless telephones to roam across large geographical regions while retaining telephonic access. Paging networks also may utilize cellular communications systems which enable a user carrying a pocket sized pager to be paged anywhere within a geographic region.
A typical cellular communications system includes a number of fixed access points (also known as base stations) interconnected by a cable medium often referred to as a system backbone. Also included in many cellular communications systems are intermediate access points which are not directly connected to the system backbone but other wise perform many of the same functions as the fixed access points. Intermediate access points, often referred to as wireless access points or base stations, increase the area within which access points connected to the system backbone can communicate with mobile devices.
Associated with each access point is a geographic cell. The cell is a geographic area in which an access point has sufficient signal strength to transmit data and receive data from a mobile device such as a data terminal or telephone with an acceptable error rate. Typically, access points will be positioned along the backbones such that the combined cell area coverage from each access point provides full coverage of a building or site.
Mobile devices such as telephones, pagers, personal digital assistants (PDA=s), data terminals etc. are designed to be carried throughout the system from cell to cell. Each mobile device is capable of communicating with the system backbone via wireless communication between the mobile device and an access point to which the mobile device is registered. As the mobile device roams from one cell to another, the mobile device will typically deregister with the access point of the previous cell and register with the access point associated with the new cell. In order to provide sufficient cell area coverage, access points within the cellular communications system typically are distributed at a separate physical locations throughout an entire building or set of buildings.
Presently radio systems transmit packets of information utilizing an Internet Protocol (IP) or other type protocol. The IP protocol includes a destination address, a source address, a length component and a data component. The data packets are stored in a queue and transmitted on a first in first out (FIFO) basis. Once a data packet is transmitted to a particular destination address, the remaining radio systems will remain idle until the entire transmission is complete. Recently a standard for wireless local area networks (WLANs) known as the IEEE 802.11 standard has been proposed and has gained acceptance among the industrial, scientific and medical communities. The IEEE 802.11 standard for WLANs is a standard for systems that operate in the 2,400-2,483.5 MHz industrial, scientific and medical (ISM) band. The ISM band is available worldwide and allows unlicensed operation of spread spectrum systems. Once a preamble of an IEEE 802.11 protocol packet is correctly received by other radio devices, they must remain off for an entire frame. This causes stations that are outside an intended transmission range to remain idle during the frame transmission reducing the entire throughput of the system.
Regardless of the type of protocol used in a cellular communication system, all devices within a range will remain off during a transmission of a packet to a destination address. In a typical radio system, if a packet is sent to a destination address and for some reason or another the packet is not properly received by the destination device, the radio system will immediately retry sending the packet a predetermined number of times before timing out. The destination device may not receive the packet because the device is turned off, the device is out of range, or for some reason or the other the packet becomes corrupted. During these retries other devices within the cell will remain idle and additional packets to be sent to other destination addresses will remain in the queue until the retries are completed. This reduces the throughput of the entire system.